Your brain is triggered by things in the sub-conscious.
For instance you listen to a movie song during the resolution of the movie, and you're extremely happy.
The next time you hear that song, you will become joyous.
So why is this, and how could you use it as an advantage? It's called anchoring, and you can anchor a feeling to experience that feeling through any sense.
This can be Visual, Audible, or Kinesthetic, or any other sense including smell and taste.
I want you to recall a movie in which the scene makes you experience an unusual feeling (happiness, sadness, adrenaline rush-ness, etc.
Then I want you to Google that scene and check what score/song was played in that scene.
Then YouTube it or buy it from iTunes, and play it.
Soon you will experience that same feeling as you felt at that time.
So why does this work? It's not because a action scene has a fast beat, or a sad scene has slow violins playing, it's because we've been anchored that feeling from he start.
If all movies had fast-paced 'rock on!' music during sad scenes, it would make us sad.
Also in a movie you are in whats called a 'trance', and our accepting an alternate reality (in this case the movie).
So it would be the same as you being in a sad part of life having a song playing.
That song will always make you sad if it was anchored by your mind (usually it does).
So the brain is much likely to anchor those feelings in your sub-conscious.
So every time you want to get happy, play a song from a happy scene from a movie (audible).
Or you can just watch that scene over again (visual).
You could also do the scene in real life (kinesthetics, or touch) or you could eat the movie (taste, and yes I'm joking).
Look around this is a powerful thing you could use to your advantage.
The next level is to anchor a feeling to someone else, secretly.